In the past some types of polymeric backbones have been transesterified with certain natural oils such as castor oil and soybean oil. These polymeric backbones have not included polylactic acid backbones. Polylactic acid backbones have been transesterified glycols or caprolactone. In both cases the hope was that the transesterification processes would lead to polymers with improved properties.
Polylactic acid is a biodegradable, solid thermoplastic aliphatic polyester that is derived from renewable resources such as corn starch; tapioca roots, chips or starch; or from sugarcane. Because it is biodegradable and renewable, there has been interest in expanding its uses. Structurally, it is a polyester with the repeating unit of —[CH(CH3)—C(O)—O]— and thus it is not a polyacid. It has been used in the manufacture of sealant films for food packaging, cups for yogurt, biomedical devices and other applications. One limitation with use of polylactic acid in more products is the fact that the polymer is a solid but has a lack of toughness and thus its usefulness is limited. Typically polylactic acid has less than 10% elongation at break. In addition, it has low solubility in many desirable solvents and when dissolved tends to have too high of a viscosity to be useful in some applications. So ways to increase the weak physical properties of the polymer have been explored. For example, it has been blended with polycarbonates or subjected to transesterification with ethylene glycol, trimethylene glycol and polycaprolactone in attempts to lower its viscosity, increase its flexibility, and change its solubility. One of the issues with blending the polylactic acids with other compounds is that this introduces the possibility of adding extractable components into the formulation which may be undesirable especially in medical or food packaging applications. The level of extractable components can raise safety and regulatory issues. Transesterification of polylactic acid with polycarbonates does not produce the desired flexibility in the final product and the cost of production is too high. The use of m-hydroxy acids, such as mandelic acid, has been used for certain specialized medical applications, but is too costly for industrial uses. The same is true of transesterification with caprolactone; it is too costly for industrial uses and the availability of caprolactone is low.
It is desirable to produce a polymeric, transesterified polylactic acid product and method of producing the same that uses biodegradable, readily available, renewable resources wherein the produced product can be a liquid at room temperature with a low viscosity. In other variations the produced product can be a waxy solid at room temperature. The produced product is relatively inexpensive to produce.